Inlet attenuator assembly



April 28, 1970 w. P. MANNING ETAL 7 3,509,568

INLET ATTENUATOR ASSEMBLY Filed July 8, 1968 I I 26 I 3 n 27 i I? I? l L J g 7 27 5 L United Patent Office 3,509,568 Patented Apr. 28, 1970 3,509,568 INLET ATTENUATOR ASSEMBLY William P. Manning, John L. Seufert, and Robert D. Strattau, Tulsa, Okla., assignors to North American Rockwell Corporation Filed July 8, 1968, Ser. No. 743,259 Int. Cl. G01s 7/42; H01q 15/18, 17/00 US. Cl. 343-18 3 Claims ABSTRACT OF THE DISCLOSURE An assembly for combination with an engine air inlet duct, such as a turbo-jet engine or ram-jet engine air inlet duct, to significantly attenuate electromagnetic energy entering at small frontal aspect angles relative to the engine face. The assembly incorporates a lattice arrangement of attenuator sheets of particular configuration to efficiently effect attenuator anti-icing with minimum adverse effect on electromagnet energy attenuation properties.

SUMMARY OF THE INVENTION A lattice of corrugated resistive/conductive attenuator strips joined together at adjacent ridge regions cooperates with a generally annular support structure for combination with an engine air inlet. Each resistive/conductive strip is provided with terminal electrical busses that are connected to a conventional electrical power supply for resistive heating purposes. The electrical bus arrangements, in combination with the necessary attenuator strip configurations, function to provide efficient anti-icing without unnecessarily decreasing assembly attenuation of entering electromagnetic energy.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an engine air inlet duct having the attenuator assembly of this invention incorporated therein;

FIG. 2 is a schematic elevational view of the lattice of attenuator strips incorporated in the assembly of FIG. 1;

FIG. 3 is a perspective view showing details for joining successive corrugated attenuator strips into the lattice arrangement of FIGS. 1 and 2;

FIG. 4 is a sectional view taken at line 44 of FIG. 3;

FIG. 5 is a perspective view of an alternate form of corrugated attenuator strip;

FIG. 6 is a sectional view taken at line 66 of FIG. 5; and

FIG. 7 is a schematic electrical diagram for the lattice arrangement of FIG. 2.

DETAILED DESCRIPTION FIG. 1 illustrates an inlet attenuator assembly 10, preferably having the features of this invention, in combination with air inlet duct 11 and turbo-jet engine 12. Assembly 10 is normally located in duct 11 forward of engine spool fairing 13 and incorporates the features of this invention in its lattice portion 14 to obtain an anti-icing capability without affectng the degree of electromagnetc energy attenuation that is otherwise achieved by such lattice portion. Although the combination is illustrated as having application to an aircraft system 15, other types of vehicular systems with other types of engines may advantageously utilize the invention.

As shown by FIG. 2 lattice 14 is located generally within annular support structure 16 and is comprised of successive corrugated resistive/conductive attenuator strips 17 joined together at adjacent ridge regions. Details of one form of satisfactory fastening arrangement are shown in FIGS. 3 and 4. The external configuration of support structure 16 corresponds to the internal configuration of duct means 11 at the zone of installation. For convenience of illustration, assembly 10 is illustrated in the drawings as having a circular external configuration. The joined attenuator strips 17 are also normally secured at their end regions to support structure 16 by conventional fastening means. The successive attenuator strips that comprise lattice 14 have electrical terminals designated A through Q in FIG. 2. Such designations correspond to the terminal designations utilized in the schematic electrical diagram of FIG. 7.

Attenuator strips 17 are each fabricated of a conventional electromagnetic energy attenuation material but in corrugated rather than flat sheet form. The material is normally a laminated construction having at least one lossy layer 18 sandwiched between protective layers 19. See FIG. 4. Lossy layer 18 is normally a fabric impregnated with a resin that includes a resistive/conductive filler such as powdered carbon or aluminum in a prescribed quantity ratio. In the instant invention lossy layer 18, in addition to functioning as an electromagnetic energy absorber, serves as a resistance element for effecting attenuator strip heating for anti-icing purposes. Protective layers 19 are generally also comprised of a fabric impregnated with a thermosetting resin and normally are non-conductive in an electrical energy sense. In most instances, the different layers utilize glass fabrics and thermosetting resins, such as a polyester resin, and are laminated into the prescribed corrugated configuration from partially cured pre-impregnated sheet materials. It is important that resistive/ conductive layer 18 be electrically continuous throughout the length of each attenuator strip 17. An electrical bus in the form of conducting Wire 20 is located within the laminate in contacting relation to resistive/conductive layer 18 at each strip end region. Such conductors electrically connect the different lossy layers 18 in lattice 14 to the various power supply terminals shown schematically in FIGS. 2 and 7.

FIGS. 3 and 4 illustrate in detail one manner for joining attenuator strips 17 together at adjacent corrugation ridge region. Non-conducting spacer elements 21, nonconducting locating pins 22, and adjacent attenuator strips 17 are assembled as illustrated. A conventional adhesive compatible with the resin systems of strips 17 and spacers 21 is used to bond the assembly elements together to complete lattice 14. Conductors 20 are preferably housed within support structure 16 for connection to an electrical power supply.

FIG. 7 schematically illustrates a method for incorporating the attenuator strips 17 of lattice 14 into an electrical power supply system. The elements of the power supply typically include, in addition to a 3-phase generator (not shown), terminal block 23, circuit breaker elements 24, and primary and secondary windings 25 and 26 of a power transformer. Current control rectifiers 27 are also typically incorporated into the system and operate in a conventional manner from a standard current controller (not shown). In the FIG. 7 arrangement, the individual attenuator strips 1'7 comprising lattice 14 are arranged to provide a nearly-balanced 3-phase load across the terminals of transformer winding 26. If operated at a frequency such as 400 cycles per second, the electrical system has minimum adverse effect on the attenuation performance of lattice 14 during anti-icing operations.

An alternate form of attenuator strip taking advantage of the features of this invention is shown in FIGS. 5 and 6. Such attenuator strip is referenced generally as 30 and utilizes the same general lossy layer/ protective layer construction shown in FIG. 4. See FIG. 6. The difference in construction for lattice 14 is that the electrical busses 31 are oriented lengthwise of the corrugated strip and preferably are positioned at a trailing edge region relative to airflow. Attenuator strip 30 differs from attenuator strip 17 primarily in the length of resistance path between conductors, the shortest distance between wires 31 along layer 18 of FIG. 5, 6 being significantly less than the shortest distance between wires 20 of the typical strip 17 in FIGS. 2, 3, 4.

We claim:

1. In an electromagnetic energy attenuator assembly having a resistance heating capability, in combination:

(a) Electrical energy power supply means,

(b) Elongated attenuator strips each having a generally rectangular planform and a corrugated configuration in evaluation, and

(c) Means joining said attenuator strips together at adjacent corrugation ridge regions in electrical y non-conducting relation.

said attenuator strips each having a continuous resistive/ conductive attenuator layer substantially coextensive with said rectangular planform and electrically connected at opposite extremes to said electrical energy power supply means for resistance heating.

2. The invention defined by claim 1, wherein said attenuator strips each have end margins and longitudinal margins substantially greater in length than said end margins, said attenuator strips being connected at opposite References Cited UNITED STATES PATENTS 2,717,312 9/1955 Taylor 343-18 2,985,880 5/1961 McMillan 34318 3,163,841 12/1964 Willett.

3,309,704 3 /1967 Klingler 3431 8 RODNEY D. BENNETT, 111., Primary Examiner B. L. RIBANDO, Assistant Examiner US. Cl. X.R. 219-209 

